Cancer currently constitutes the second most common cause of death in the United States, and cancer is difficult to diagnose and treat effectively. Accordingly, there is a need in the art for improved methods for detecting and treating various cancers. The present invention fulfills these needs and further provides other related advantages, such as uses related to the treatment of other diseases.
Breast Cancer
Breast cancer is the primary killer of women. One in eight American women will develop breast cancer in her lifetime. An estimated 3 million women in the U.S. today are living with breast cancer, which 2 million have been diagnosed with the disease and 1 million have the disease but do not yet know it.
The incidence of breast cancer in the U.S. has more than doubled in the past 30 years. In 1964, the lifetime risk was one in twenty. Today it's one in eight. Breast cancer is the most commonly diagnosed cancer in women in both America and worldwide. One or more of a variety of treatments such as surgery, radiotherapy, chemotherapy and hormone therapy are used. The treatment course for a certain type of breast cancer is usually selected based on a various prognostic parameters, for example, an analysis of specific tumor markers. (e.g. Porter-Jordan and Lippman, Breast Cancer 8:73-100 (1994)). However, the use of established markers is insufficient to interpret the results and it still results in high mortality which is observed in breast cancer patients. Despite considerable research into therapies for these and other cancers, breast cancer remains difficult to diagnose and treat effectively. Accordingly, there is a need in the art for improved methods for detecting and treating such cancers.
Lung Cancer
Lung cancer is the second most prevalent type of cancer for both men and women in the United States and is the most common cause of cancer death in both sexes. Lung cancer can result from a primary tumor originating in the lung or a secondary tumor which has spread from another organ such as the bowel or breast. The five-year survival rate for lung cancer continues to be poor at 8-15% survival indicating a large unmet need with regard to more effective treatments and better diagnosis. The estimated total lung cancer deaths in the U.S. in 2003 are 157,200 and the total estimated new cases in 2003 are 171,900. Primary lung cancer is divided into three main types; small cell lung cancer; non-small cell lung cancer; and mesothelioma. Small cell lung cancer is also called “Oat Cell” lung cancer because the cancer cells are a distinctive oat shape. There are three types of non-small cell lung cancer. These are grouped together because they behave in a similar way and respond to treatment differently to small cell lung cancer. The three types are squamous cell carcinoma, adenocarcinoma, and large cell carcinoma. Squamous cell cancer develops from the cells that line the airways. Adenocarcinoma also develops from the cells that line the airways. However, adenocarcinoma develops from a particular type of cell that produces mucus (phlegm). Large cell lung cancer has been thus named because the cells look large and rounded when they are viewed under a microscope. Mesothelioma is a rare type of cancer which affects the covering of the lung called the pleura. Mesothelioma is often caused by exposure to asbestos.
Secondary lung cancer is cancer that has started somewhere else in the body (for example, the breast or bowel) and spread to the lungs. Choice of treatment for secondary lung cancer depends on where the cancer started. In other words, cancer that has spread from the breast should respond to breast cancer treatments and cancer that has spread from the bowel should respond to bowel cancer treatments.
The stage of a cancer indicates how far a cancer has spread. Staging is important because treatment is often decided according to the stage of a cancer. The staging is different for non-small cell and for small cell cancers of the lung.
Non-small cell cancer can be divided into four stages. Stage I is very localized cancer with no cancer in the lymph nodes. Stage II cancer has spread to the lymph nodes at the top of the affected lung. Stage III cancer has spread near to where the cancer started. This can be to the chest wall, the covering of the lung (pleura), the middle of the chest (mediastinum) or other lymph nodes. Stage IV cancer has spread to another part of the body.
Since small cell lung cancer can spread quite early in development of the disease, small cell lung cancers are divided into only two groups. These are: limited disease, that is cancer that can only be seen in one lung and in nearby lymph nodes; and extensive disease, that is cancer that has spread outside the lung to the chest or to other parts of the body. Further, even if spreading is not apparent on the scans, it is likely that some cancer cells will have broken away and traveled through the bloodstream or lymph system. To be safe, it is therefore preferred to treat small cell lung cancers as if they have spread, whether or not secondary cancer is visible. Because surgery is not typically used to treat small cell cancer, except in very early cases, the staging is not as critical as it is with some other types of cancer. Chemotherapy with or without radiotherapy is often employed. The scans and tests done at first will be used later to see how well a patient is responding to treatment.
Procedures used for detecting, diagnosing, monitoring, staging, and prognosticating lung cancer are of critical importance to the outcome of the patient. For example, patients diagnosed with early lung cancer generally have a much greater five-year survival rate as compared to the survival rate for patients diagnosed with distant metastasized lung cancer. New diagnostic methods which are more sensitive and specific for detecting early lung cancer are clearly needed.
Lung cancer patients are closely monitored following initial therapy and during adjuvant therapy to determine response to therapy and to detect persistent or recurrent disease of metastasis. There is clearly a need for a lung cancer marker which is more sensitive and specific in detecting lung cancer, its recurrence, and progression.
Another important step in managing lung cancer is to determine the stage of the patient's disease. Stage determination has potential prognostic value and provides criteria for designing optimal therapy. Generally, pathological staging of lung cancer is preferable over clinical staging because the former gives a more accurate prognosis. However, clinical staging would be preferred were it at least as accurate as pathological staging because it does not depend on an invasive procedure to obtain tissue for pathological evaluation. Staging of lung cancer would be improved by detecting new markers in cells, tissues, or bodily fluids which could differentiate between different stages of invasion.
Pancreatic Cancer
The prognosis for pancreatic carcinoma is, at present, very poor. Pancreatic cancer displays the lowest five-year survival rate among all cancers. Such prognosis results primarily from delayed diagnosis, due in part to the fact that the early symptoms are shared with other more common abdominal ailments. Despite the advances in diagnostic imaging methods like ultrasonography (US), endoscopic ultrasonography (EUS), dualphase spiral computer tomography (CT), magnetic resonance imaging (MRT), endoscopic retrograde cholangiopancreatography (ERCP) and transcutaneous or EUS-guided fine-needle aspiration (FNA), distinguishing pancreatic carcinoma from benign pancreatic diseases, especially chronic pancreatitis, is difficult because of the similarities in radiological and imaging features and the lack of specific clinical symptoms for pancreatic carcinoma.
Substantial efforts have been directed to developing tools useful for early diagnosis of pancreatic carcinomas. Nonetheless, a definitive diagnosis is often dependent on exploratory surgery which is inevitably performed after the disease has advanced past the point when early treatment may be effected.
Colon Cancer
The prognosis of colon cancer is directly related to the degree of penetration of the tumor through the bowel wall and the presence or absence of nodal involvement, consequently, early detection and treatment are especially important. Currently, diagnosis is aided by the use of screening assays for fecal occult blood, sigmoidoscopy, colonoscopy and double contrast barium enemas. Treatment regimens are determined by the type and stage of the cancer, and include surgery, radiation therapy and/or chemotherapy. Recurrence following surgery (the most common form of therapy) is a major problem and is often the ultimate cause of death. In spite of considerable research into therapies for the disease, colon cancer remains difficult to diagnose and treat. In spite of considerable research into therapies for these and other cancers, colon cancer remains difficult to diagnose and treat effectively. Accordingly, there is a need in the art for improved methods for detecting and treating such cancers.
Prostate Cancer
Prostate diseases include, for example, prostate cancer, as well as benign prostatic hyperplasia (BPH) and prostatitis.
Prostate cancer is the most common non-skin cancer in the United States, where one in six American men develop prostate cancer during his lifetime. About 80% of prostate cancers are diagnosed in men over the age of 65. African-American men are 65% more likely to develop prostate cancer than Caucasian-American men and, furthermore, African-American men tend to get more severe forms of prostate cancer and are more than twice as likely to die from prostate cancer as are Caucasian-American men. Approximately 25% of men with prostate cancer have a family history of prostate cancer. The risk of prostate cancer doubles among men having a first-degree relative with the disease; with two close relatives, a man's risk increases fivefold; and with three or more close relatives, the risk for developing prostate cancer is almost 100%.
Screening for prostate cancer is typically carried out using the prostate specific antigen (PSA) blood test and the digital rectal exam (DRE). The DRE and PSA test cannot confirm whether or not prostate cancer is present, but can indicate whether further testing is needed. If either the DRE or the PSA test indicates the presence of prostate cancer, a transrectal ultrasound (TRUS)-guided biopsy is typically carried out. A biopsy is the only way to confirm or diagnose the presence of prostate cancer. During a biopsy, a TRUS is used to view and guide one or more needles into the prostate to take multiple small samples of tissue from different parts of the prostate. These tissue samples are then examined for the presence of cancer in order to generate a value known as a Gleason Grade, which characterizes the aggressiveness of a particular prostate tumor based on the microscopic appearance of the tissue. Prostate cancer is also staged, which is an assessment of the size and degree of metastases of prostate cancer, using either of two different staging systems (a traditional system classifies the disease into four clinical categories rated A through D; another system exists which is called TNM staging for Tumor-Nodes-Metastases staging). The major treatment options for prostate cancer include hormonal therapy, surgery, radiation therapy, and chemotherapy. Early detection of prostate cancer increases the success rate of these treatment options.
Stomach (Gastric) Cancer
Stomach diseases (also known as gastric diseases) include, for example, stomach cancer and ulcers (ulcers typically involve a break in the tissue lining the stomach).
Stomach cancer is the second most common cancer in the world, behind only skin cancer. Stomach cancer occurs twice as often in men as women and is the most prevalent carcinoma in East Asia, with the rate in Japan being more than seven times that in the United States and accounting for one-third of all cancer deaths in Japan. The average age of individuals afflicted by stomach cancer is 55 years of age.
Several different types of stomach cancer exist. Adenocarcinomas are the most common type of stomach cancer, accounting for 90-95% of malignant tumors of the stomach. Adenocarcinomas typically develop from the epithelial cells that form the innermost lining of the stomach's mucosa. Soft tissue sarcomas are another type of stomach cancer, and soft tissue sarcomas typically develop from the cells of the muscle layer of the stomach. Leiomyosarcoma is the most common type of soft tissue sarcoma that affects the stomach. Another type of sarcoma that can affect the stomach is a gastrointestinal stromal tumor (GIST). Lymphomas can also affect the stomach, of which MALT (mucosa-associated lymphoid tissue) lymphoma is the most common type of lymphoma that affects the stomach. The stomach can also be affected by carcinoid tumors.
Stomach cancer can be diagnosed by an upper gastrointestinal (GI) series, which are x-rays of the esophagus and stomach taken after the patient has drinken a barium solution. Alternatively, an endoscopy can be carried out in which a tube is passed through the esophagus into the stomach and, if desired, a biopsy can be done to obtain a tissue sample for laboratory analysis. Blood tests, chest x-rays, a CT scan of the abdomen, and a check for blood in the patient's stools may also be carried out. Treatment for stomach cancer can include a combination of surgery (termed “gastrectomy”), chemotherapy, and radiation therapy. If the tumor is located close to the small intestine, a partial gastrectomy may be carried out in which a portion of the stomach is removed. If the tumor is located closer to the esophagus, a near-total gastrectomy may be carried out.
Stomach cancer is staged based on how deep the tumor has penetrated the stomach lining, whether it has invaded surrounding lymph nodes, and whether it has metastasized. The system most often used to stage stomach cancer in the United States is the American Joint Commission on Cancer (AJCC) TNM system. T indicates how far the tumor has grown within the stomach and into nearby organs, N indicates the degree to which the tumor has spread to lymph nodes, and M indicates the degree to which the tumor has metastasized to distant organs. In TNM staging, information about the tumor, lymph nodes, and metastasis is combined in a process called stage grouping in order to indicate a stage (represented by stages 0, I, IIA, IIB, III, IVA, and IVB). As the stage increases from 0 to IV, the 5-year relative survival rates for patient's diagnosed with stomach cancer at each stage decreases from about 89% (for stage 0) to about 7-8% (for stages IVA and IVB).
Kidney Cancer
The American Cancer Society estimates that there will be about 36,160 new cases of kidney cancer (22,490 in men and 13,670 in women) in the United States in the year 2005, and about 12,660 people (8,020 men and 4,640 women) will die from this disease. Kidney cancer (also referred to as renal cancer or renal cell carcinoma) mostly affects adults between 50 and 70 years of age. If detected early, kidney cancer is curable. However, symptoms may not appear until the tumor has grown to a large size or metastasized to other organs, at which point treatment is difficult.
The 5-year survival rate for individuals diagnosed with kidney cancer is about 90% for those individuals whose tumor is confined to the kidney, about 60% if it has only spread to nearby tissues, and about 9% if it has spread to distant sites (American Cancer Society, Detailed Guide: Kidney Cancer. “What Are the Key Statistics for Kidney Cancer (Renal Cell Carcinoma)?”).
The majority of kidney cancers are renal cell carcinomas (which accounts for over 90% of malignant kidney tumors), also known as renal adenocarcinomas or clear cell carcinomas. There are five main types of renal cell carcinoma that are identified based on microscopic examination of cell type: clear cell, papillary, chromophobe, collecting duct, and “unclassified.” Kidney cancers are also usually graded on a scale of 1 through 4 to indicate how similar the nuclei of the cancer cells are to the nuclei of normal kidney cells (grade 1 renal cell cancers have cell nuclei that differ very little from normal kidney cell nuclei and generally have a good prognosis, whereas grade 4 renal cell cancer nuclei look considerably different from normal kidney cell nuclei and have a worse prognosis). In addition to grade, kidney cancers are also characterized by stage, which describes the size of the cancer and degree of metastasis. The most commonly used staging system is that of the American Joint Committee on Cancer (AJCC) (also referred to as the TNM system), although the Robson classification is an older system that may be occasionally used.
In additional to renal cell carcinomas, other types of kidney cancers include transitional cell carcinomas, Wilms tumors, and renal sarcomas. Wilms tumors are the most common type of kidney cancer in children and are extremely rare in adults. Benign (non-metastasizing) kidney tumors include renal cell adenomas, renal oncocytomas, and angiomyolipomas (American Cancer Society, Detailed Guide: Kidney Cancer. “What Is Kidney Cancer (Renal Cell Carcinoma)?”).
Risk factors for kidney cancer include the following: age older than 50 years; male (men are twice as likely to get kidney cancer compared to women); cigarette smoking; exposure to asbestos, cadmium, or organic solvents; obesity; a high-fat diet; and von Hippel-Lindau disease (a genetic condition that has a high incidence of kidney cancer).
Symptoms of kidney cancer include hematuria (blood in the urine), abdominal or low back pain, weight loss, fatigue, anemia, fever, high blood pressure, and leg or ankle swelling.
In addition to a detailed medical history, physical examination, and laboratory blood testing, diagnosis of kidney cancer may typically include a computed tomography (CT) scan, ultrasound, magnetic resonance imaging (MRI), intravenous pyelography (a kidney test that utilizes dye and x-rays), or arteriography (a test in which dye is applied to the blood vessels feeding the kidney). To detect metastatic disease, chest X-ray and bone scan may be implemented.
Treatment of kidney cancer in individuals whose tumor is confined to the kidney may involve surgical removal of the kidney (nephrectomy) and surrounding tissue. Radiation therapy may be applied to treat pain and advanced or metastatic kidney cancers or to help shrink a tumor that is causing obstruction. Immunotherapy, such as interferon and interleukin-2, may be used to boost the immune system in patients with advanced kidney cancer (Journal of the American Medical Association, JAMA Patient Page: Kidney Cancer).
Liver Cancer
Liver diseases include, for example, liver cancer and liver cirrhosis. Liver cancers include malignant liver tumors such as hepatocellular carcinoma (which is the most common type of liver cancer, accounting for about 75% of primary liver cancers) and cholangiocarcinomas, as well as benign liver tumors such as hemangioma, hepatic adenomas, and focal nodular hyperplasia. Among other risk factors (e.g., cirrhosis, such as from alcohol abuse), chronic infection with hepatitis B or hepatitis C virus is a significant liver cancer risk factor.
Furthermore, when cancer is found in the liver, it is often the case that the cancer did not originate in the liver but rather spread to the liver from another cancer that began in a different part of the body. The liver is a common site of metastases for cancers in other organs (such as cancers of the lung, breast, colon, and rectum), particularly since the liver receives blood from the abdominal organs via the portal vein. Tumor cells may detach from the primary cancer, enter the bloodstream or lymphatic channels, and travel to the liver where the tumor cells begin to grow independently.
Liver cancer is rarely diagnosed at an early stage because it usually does not cause symptoms until the cancer is in its later stages and, because no screening tests exist, small tumors are difficult to detect by physical exams. Liver cancers can sometimes be detected using a blood test for alpha-fetoprotein (AFP). However, some tumors do not produce AFP in quantities significant enough to be detected until the tumor is too large to be removed or has metastasized outside the liver. In addition to blood tests for AFP, other diagnostic techniques that may be used to detect liver cancer include ultrasound, CT scans, MRI, angiography, laparoscopy, and biopsy.
Once diagnosed, liver cancer is typically characterized by a stage using Roman numerals I through IV, with a higher numeral indicating a more serious cancer. Stage III is further sub-divided into A, B, and C.
The three main types of treatment for liver cancer are surgery, radiation therapy, and chemotherapy. Currently, surgery offers the only chance of completely curing liver cancer. However, surgery can only completely cure liver cancer if the cancer is small and can be entirely removed. Unfortunately, complete removal of most liver cancers is not possible. Often the cancer is too large by the time it is detected, is present in many different parts of the liver, or has metastasized beyond the liver. Also, many patients who have cirrhosis do not have enough healthy liver remaining for surgery to even be an option. Radiation therapy may be used to shrink a liver tumor or to provide relief from symptoms such as pain, but it can not cure liver cancer and may not prolong survival for liver patients. With regards to chemotherapy, liver cancer does not respond to most drugs. The most successful single drug has been doxorubicin (Adriamycin), however studies generally have not shown that chemotherapy prolongs survival for liver cancer patients.
Only a small fraction of liver cancers are detected at an early stage and can be successfully removed by surgery. Less than 30% of patients who undergo surgery have their cancer completely removed. The overall 5-year relative survival rate from liver cancer is approximately 7%.
Melanoma (Skin Cancer)
Skin cancer includes, for example, melanoma. Melanoma is a type of cancer in which melanocytes (pigment cells) become cancerous. Melanoma generally originates in the skin (cutaneous melanoma), however melanoma can sometimes originate in other areas of the body where melanocytes are present, such as the eyes, meninges, digestive tract, and lymph nodes. Other types of skin cancer include basal cell and squamous cell cancers. Melanoma is much more likely to metastasize and to be fatal than other types of skin cancer.
Melanoma is increasing in occurrence in the United States and worldwide faster than any other cancer, with an approximately 3% annual increase in new cases. The risk for melanoma in the year 2000 was 1 in 74, and melanoma is the most common cancer in individuals aged 20-30 and the most common cause of cancer death in women age 25-30 (and #2 cause of death, after breast cancer, for women age 30-35). Melanoma accounts for 5% of all skin cancers, but 71% of all skin cancer deaths. However, the earlier that melanoma is diagnosed, the better the prognosis for survival.
Thus, it is clear that early detection of cancer is desirable. Furthermore, it would also be desirable to identify individuals who have an increased risk of developing cancer in the future. Additionally, novel therapeutic agents are needed for treating cancer.
One promising method for early diagnosis of various forms of cancer is the identification of specific biochemical moieties, termed targets, expressed differentially in cancerous cells. The targets may be either cell surface proteins, cytosolic proteins, or secreted proteins. Antibodies or other biomolecules or small molecules that will specifically recognize and bind to the targets in the cancerous cells potentially provide powerful tools for the diagnosis and treatment of the particular malignancy.
GFRa1
GFRa1 is a cystein-rich glycosyl phosphatidylinositol (GPI)-linked ligand binding cell surface receptor. GFRa1 is a member of a family of GFRa receptors that share a common signaling receptor tyrosine kinase subunit c-RET. GFRa1 is the preferred binding partner of glial-cell-line-derived neutrophic factor (GDNF). Following binding with GDNF, GDNF-GFRa1 forms a dimer that can interact with a kinase receptor called c-Ret. Activation of c-Ret triggers transphosphorylation of specific tyrosine residues and activation of intracellular signaling cascades that regulate cell survival, differentiation, proliferation, migration, chemotaxis, branching morphogenesis, neurite outgrowth, and synaptic plasticity. Alternatively, GDNF-GFRa1 dimer can interact with NCAM to initiate signaling. Studies have shown that GDNF-activated N-CAM signaling acts to promote CNS axon growth and Schwann cell migration.
Claudin-4
Claudin-4 is part of a superfamily (24 family members) of tight junction (TJ) related proteins. Claudin-4 is involved in cell-cell adhesion and has an extracellular domain larger than 40 amino acids. Claudins are one of three types of tight-junction cell adhesion proteins (occludin, JAM, claudins) and thought to be the most critical for constituting tight-junction strands. Tight junctions form barriers at epithelial and endothelial cells. Tight junctions regulate cellular movement of water and ions (intracellular sealing) and limit lateral diffusion of lipids and proteins between the apical and basolateral membrane regions to form polarized epithelia. Aggregated TJ proteins form networks of paired TJ strands between each plasma membrane at discrete sites of fusion of plasma membranes of adjacent cells. Each TJ strand associates laterally with another TJ strand in the plasma membrane of an adjacent cell to form a paired TJ strand.
Ion transport is charge- and size-selective with ion transport across tight-junctions. Cation selective transport is mainly by the paracellular pathway, and may be coupled with transcellular transport in certain situations. Activation of Na+-glucose transporters in the intestine is thought to alter structure and function of tight-junctions. With elevated glucose levels, absorption of glucose occurs by transport through tight-junctions when Na+-glucose transporters are saturated.
Macromolecular protein complexes form at tight-junctions. Proteins with a PDZ domain bind to the cytoplasmic surface of tight-junctions by direct interaction with the carboxyl terminus of claudins. This functions to cross-link TJ strands to actin cytoskeleton, and plays a role in regulating paracellular transport across tight-junctions. These proteins also function as adaptor proteins to recruit signaling molecules for activation of downstream signal transduction pathways, and play a role in cell-matrix adhesion with formation of a complex at integrin-based adhesion sites. For a further review, see Tsukita et al., “Multifunctional strands in tight junctions”, Nat Rev Mol Cell Biol. 2001 April; 2(4):285-93.
Altered permeability of tight junctions associated with multiple pathological states, including inflammation (e.g., inflammatory bowel disease) and tumorigenesis. Claudin-4 functions as a receptor for Clostridium perfringens enterotoxin (CPE), which is known to injure intestinal epithelial cells and breast cancer cells by increasing membrane permeability, thereby resulting in loss of osmotic equilibrium leading to cell death (Katahira et al. JCB 1999; Kominsky et al. Am J Pathol 2004). Cytotoxic effects of CPE appears to be restricted to Claudin-4 expressing cells (demonstrated in pancreatic cancer), and has been proposed as a novel treatment for Claudin-4 expressing solid tumors (Leder et al. Gastroenterology 2001).
Altered regulation of claudin-4 occurs in multiple cancers. For example, EGF signaling through the Ras signaling pathway increases protein synthesis of several claudins, including Claudin-4 (Singh et al. JBC 2004). Claudins have been shown to activate pro-matrix metalloproteinase-2 through direct interactions, and Claudin-4 recruits membrane-type matrix metalloproteinases on cell surfaces to high focal concentrations of enzymes for activation of MMP-2 (Miyamori et al. JBC 2001).
Claudin-4 is involved in cancer biology. For example, increased claudin-4 expression occurs in multiple tumor types [e.g., pancreatic cancer (Leder et al. Gastroenterology 2001), prostate cancer (Long et al. Cancer Res 2001), ovarian carcinoma (Santin et al. Int J Cancer 2004; Hibbs et al. Am J Pathol 2004), and squamous cell carcinoma (keratinized tumors) (Morita et al. Br J Dermatol 2004)]. Overexpression of Claudin-4 in pancreatic cancer correlates with decreased invasiveness in vitro (Boyden chamber) and in vivo (mouse lung colonization assay) (Michl et al. Cancer Res 2003). Reduced expression of claudin-4 and E-cadherin correlates with poor differentiation in gastric cancer (Lee et al. Oncol Rep 2005). Claudin-4 and claudin-3 are expressed in greater than 90% of breast carcinomas, but no correlation has been found with estrogen or progesterone receptor status or with tumor grade (Soini et al. Hum Pathol 2004).
Thus, Claudin-4 is involved in cell-cell adhesion, overexpression of Claudin-4 is documented in the literature in several cancers, Claudin-4 is overexpressed in greater than 90% of breast carcinomas, and Claudin-4 is potentially involved in regulating metastasis and the invasive potential of cancer cells.
ASCT2
ASCT2, also known as Neutral Amino Acid Transporter (NAAT), is a cell surface transporter involved in cellular metabolism. ASCT2 has an extracellular domain that is larger than 100 amino acids in size. Antagonism of ASCT2 function stimulates apoptosis.
ASCT2, which is a member of the ASC amino acid transporter system, is a Na+ dependent transporter with high affinity for glutamine. ASCT2 also transports other zwitterionic amino acids such as serine, threonine, cysteine, alanine, and asparagine. Glutamine is an essential metabolic intermediate required for cellular growth. Glutamine requirements are increased in rapidly dividing tumor cells (M A Medina. 2001. J Nutr 131(9 Suppl):2539S-2542S).
Hepatoma-specific expression of ASCT2 is reported in the literature. ASCT2 is not expressed in normal liver tissue. In hepatocellular carcinoma, glutamine uptake is 10-30 times faster than in normal hepatocytes. Antisense knockdown of ASCT2 expression resulted in induction of apoptosis in hepatoma cells (B C Fuchs, et al. 2004. Am J Physiol Gastrointest Liver Physiol 286:G467-G478).
Expression of ASCT2 in colorectal adenocarcinoma is reported in the literature. ASCT2 protein was detected by western blot using MYZ polyclonal antibodies in colon tumor lysates. Immunohistochemistry (IHC) was performed on 63 colon tumor samples, with the following results: negative 41%, 1-25% of cell positive 24%, 26-50% of cells positive 13%, and greater than 50% of cells positive 22%. ASCT2 expression was associated with decreased patient survival (p=0.0002) (D Witte, et al. 2002. Anticancer Res 22:2555-2558).
Expression of ASCT2 in prostate is reported in the literature. IHC was performed using MYZ polyclonal antibodies on 640 prostate samples [normal, benign prostatic hyperplasia (BPH), and adenocarcinoma]. High level of ASCT2 expression was found in 49% normal, 25.8% BPH, and 25.3% adenocarcinoma. Significant decrease in ASCT2 expression in BPH and adenocarcinoma compared to normal prostate was observed. Higher ASCT2 expression was associated with poor prognostic factors, aggressive behavior, and poor survival (R Li, et al. 2003. Anticancer Res 23:3413-3418).
CD166 (ALCAM)
ALCAM (interchangeably referred to as CD166) is a member of the immunoglobulin superfamily IgSF. ALCAM is expressed in a subset of activated leukocytes, monocytes, fibroblasts, epithelial, and neural cells. The extracellular region of ICAM (typically about 527 amino acids in size) consists of five Ig-like domains. The two N-terminal domains closely resemble variable-type (V-) domains while the three following domains are more similar to the constant (C-) domains. ICAM has a short intracellular domain that is typically about 32 amino acids in size.
ALCAM is involved in both homophilic adhesion and heterophilic adhesion to CD6, which is a member of the scavenger receptor cysteine-rich superfamily. ALCAM may also bind NgCAM and HDL. CD6 is a member of the scavenger receptor cysteine-rich superfamily. CD6 is expressed on thymocytes, mature T-cells, and some B cells. Adherence of CD6+ thymocytes to ALCAM-expressing thymic epithelial cells is important for the differentiation and development of mature T cells. Interaction of CD6+ mature T cells and CD166-expressing monocytic antigen presenting cells is important for T cell activation. T cell activation can be inhibited by addition of monomeric, soluble forms of CD6 or CD166.
ALCAM homophilic interactions are important in the homing of hematopoietic stem cells on to stromal cells, thereby playing an important role in the regulation of hematopoietic development. Clustering of ALCAM at the cell surface is regulated by the actin cytoskeleton and the stabilization of this clustering may involve PKCa.
ALCAM contains a diSia epitope. diSia epitopes play an important role in neurite extension. Inhibition of this epitope using mAbs can specifically inhibit neurite formation.
CD166−/− mice are viable, fertile, and display no gross external morphological defects, however axon fasciculation defects and retinal dysplasias are observed. No obvious defects in circulating lympohocytes are observed, but preliminary analysis reveals histological abnormalities of the spleen (Mol Cell Neurosci (2004) 59-69).
It has been demonstrated that ALCAM derived from an A375 melanoma line contains GlcNAc beta 1-6 branched oligosaccharides, which is a sugar moiety associated with metastatic potential (Melanoma Res (2004) 14 479-485).
scFV, mAb, and CD6-Fc all induce ALCAM internalization into an ovarian carcimoma line. scFv-saporin immunotoxin selectively kills cell lines expressing ALCAM (J Cell Sci (2005) March 15).
Regarding the role of CD166 (ALCAM) in tumor biology, CD166 is a marker of tumor progression in primary malignant melanoma (MM). 4/38+ve (benign)−17/23+ve late stage (MM)−13/28 metastasis (Am J Path (2000) 15 769-774). CD166 is overexpressed in colorectal carcinoma and correlates with shortened patient survival (J Clin Path (2004) 57: 1160-1164). Expression of CD166 is associated with poor prognosis in bladder cancer (UroOncology (2003) 3 121-129). CD166 is upregulated in low-grade prostate cancer and progressively lost in high-grade lesions (The Prostate (2003) 54 34-43). In two breast cancer studies, CD166 expression appeared elevated in early stage tumors (PR+/ER+) (Breast Cancer Res (2004) δ 478-487). Anti-ALCAM antibody decreased proliferation in breast cancer cells and reduced adhesion (FASEB J (2004) 18 A330).
For a further review of ALCAM, see also J. Biol. Chem. (2004) 279 55315-55323.
CD55
CD55 is a membrane-associated complement regulatory protein and has an extracellular domain that is typically larger than 300-400 contiguous amino acids. CD55 is involved in immune modulation and functions to protect cells from bystander attack by blocking the complement cascade.
CD55 recognizes C4b and C3b fragments which are locally generated during C4 and C3 activation. Interaction of DAF with cell-associated C4b and C3b polypeptides interferes with their ability to catalyze the conversion of C2 and factor B to enzymatically-active C2a and Bb and thereby prevents the formation of C4b2a and C3bBb, which are the amplification convertases of the complement cascade.
CD55 is expressed on all serum-exposed cells (red blood cells, leukocytes, endothelial cells and epithelial cells), and the soluble form is present in body fluids and extracellular matrix (serum level ˜30 ng/ml) (C. Makidono et al., 2004. J Lab Clin Med 143:152-158).
CD55 is a possible ligand for CD97 (upregulated on most leukocytes during activation), which may serve as an adhesion mechanism (J. Hamann et al., 1996. J Exp Med 184:1185-1189).
Complement regulatory proteins are commonly deregulated in tumor cells. Through over-expression of CD55, CD46, CD35 and/or CD59, tumor cells are able to protect themselves for complement-mediated lysis, which is a major limitation to immunotherapeutic treatments.
CD55 is associated with poor prognostic indicator in colorectal carcinoma. High CD55 levels are associated with a 24% survival rate, and low CD55 levels are associated with a 50% survival rate (L. G. Durrant, et al., 2003. Cancer Immunol Immunother 52(10):638-42).
CD55 is upregulated in gastric carcinomas (T. Kiso et al., 2002. Histopathology 40:339-347). Also, loss of CD55 is associated with aggressive breast tumors (Z. Madjd, et al. 2004. Clin Cancer Res 10(8):2797-803).
CD55 is cleaved from a GPI anchor in colorectal carcinomas and can be detected in stool samples, and is therefore possibly useful as a diagnostic (M. Kawada et al. 2003. J Lab Clin Med 142:306-312).
Human IgM antibody (SC-1) against a tumor-specific form of CD55 has been isolated from a gastric carcinoma patient. The antigenic site of SC-1 is an N-linked carbohydrate residue. SC-1 induces specific apoptosis of gastric carcinoma cells both in vitro and in vivo (F. Hensel et al., 1999. Cancer Res 59:5299-5306). SC-1 was successfully used in a phase I/II clinical study, showing induction of regression and apoptosis in primary gastric carcinomas with minimal toxicity (H. P. Vollmers et al., 2004. J Clin Oncol 22:4070 (Abstract)).
Antibody that was raised against an osteosarcoma cell line was used for clinical imaging of over 300 patients with colorectal, gynecologic, and gastrointestinal lesions in the 1980s. The antibody detected lesions as small as 1 cm3 in 70% of patients. The antigen for this antibody is CD55.
Anti-CD55 mAb significantly enhanced activity of Rituxan (Biogen IDEC, anti-CD20 for NHL) when used together in a cell-based study (Viragen).
Human anti-idiotypic antibody that mimics CD55 has been used successfully in over 200 colorectal and osteosarcoma patients (D. T. J. Buckley et al., 1995. Hum. Antibody Hybridoma 6:68-72).
Transglutaminase 2 (TG2)
Transglutaminase 2 (TG2) is a member of the transglutaminase family of enzymes that catalyses Ca2+ dependent reactions, resulting in the modification of glutamine and lysine residues. TG2 contains a large extracellular domain that is typically greater than 200 amino acids in size.
At membrane locations, TG2 can act as a G-protein to mediate transmembrane signaling. Gh/TG2 couples a1b and a1d adrenoreceptors, thromboxane and oxytocin receptors to phospholipase C, mediating inositol phosphate production in response to agonist activation. TG2 can also act as an isopeptidase in a Ca2+-dependent manner. Thus, TG2 is able to modify major components of the cytoskeleton. TG2 is externalized from cells where it mediates the interaction of integrins with fibronectin and cross-links proteins of ECM. This function has implications in adhesion and spreading. Under certain conditions, TG2 translocates to the nucleus and functions as a G-protein or as a transamidase that cross-links histones. Thus, TG2 may have a role in chromatin modification or gene expression regulation.
CD49f
CD49f (integrin α6) is a cell surface receptor with an extracellular domain that is typically larger than 1000 amino acids in size. This protein functions as a receptor for laminin.
The α6 chain is found in only two heterodimeric combinations, α6β1 and α6β4. The α6β1 integrin (VLA-6) binds laminins-1, -2 and -4, while α6β4 binds laminin-1 and, with higher affinity, laminin-5 (Eur. J. Biochem, 1991; 199:425). The α6β4 integrin is found mainly in hemidesmosomes, and the large cytoplasmic domain of the β4 integrin is important in the integrity of these structures (EMBO J, 1990; 9:765). Mice lacking either α6 or β4 genes display perinatal lethality (Genes Dev, 1995; 9:1883).
CD49f contributes to breast carcinoma survival and progression (Mol Cells, 2004; 17:203) and is over-expressed in human esophageal carcinomas (Int J. Oncol, 2000; 16:725) and human pancreatic carcinoma (Cancer Lett, 1997; 118:7). CD49f is also expressed in human pulmonary squamous cell and adenocarcinomas (Hum Pathol, 1998; 29: 1208). In hepatocellular carcinoma, CD49f exhibits differential display and messenger RNA overexpression (Hepatology, 1995; 22: 1447). CD49f is associated with a migratory and invasive phenotype in human prostate carcinoma cells (Clin Exp Metastasis, 1995; 13: 481).
CD98
CD98 (4F2hc) (SLC3A2; solute carrier family 3 member 2 isoform A) belongs to a family of glycoprotein-associated amino acid transporters. CD98 has an extracellular domain that is typically greater than 400 amino acids in size and functions as a sodium-independent transporter for cellular uptake of large neutral amino acids. CD98 has been implicated in hematopoietic and osteoblast cell differentiation.
CD98 has been shown to be associated with CD147, ASCT2, and β1 integrin (CD29), which is involved in CD98-induced cell aggregation. Through association with integrin, CD98 plays a role in cell adhesion, modulating the signaling for tumor cell proliferation and anchorage independent growth. The association of CD98 with integrin α4β1 is involved in T-cell activation.
In its interaction with CD98, CD147 may act as an ancillary adhesion molecule mediating cell-cell binding. CD147 may inhibit CD98 signaling for homotypic aggregation by blocking CD98-induced tyrosine phosphorylation. Additionally, a CD98-CD147 complex may mediate cell proliferation as indicated by RNA interference (RNAi) knockdown
In several cancers such as salivary adenoid cystic carcinoma, oral squamous cell carcinoma, squamous cell carcinoma of the larynx and gliomas, CD98 is overexpressed. Sequiterpene lactone cynaropicrin inhibits activation of β1 integrin and CD98 aggregation by downregulating expression of β1 integrin and CD147 and blocking downstream the ERK signaling cascade and rearrangements of the cytoskeleton. The compound has anti-inflammatory and immunomodulatory effects and is cytotoxic and pro-apoptotic in cancer cells.
CD104 (β4 Integrin)
β4 integrin (CD104) is a Type I membrane protein comprising an extracellular domain typically greater than 500 amino acids and a large cytoplasmic domain typically greater than 1000 amino acids that contains 4 fibronectin type III domains. Five alternate splice forms of β4 integrin (β4A-β4E) have been identified. β4 integrin associates with integrin α6 to form the heterodimer integrin α6/β4, which is a receptor for laminin-5. α6/β4 uses laminin 5 anchoring filaments to attach an epithelium to the basal lamina to form hemidesmosomes. [J Cell Bio (1991) 113: 907-917]
Ligation of α6/β4 causes phosphorylation of the cytoplasmic tail of β4 through activation of an integrin-associated Src family kinase, causing recruitment of Shc and activation of Ras and PI-3K. The phosphorylation of β4 causes disruption of hemidesmosomes [J Biol Chem (2001) 276: 1494-1502], [Cancer Cell (2004) δ: 471-483]. The N-terminus of the β4 cytoplasmic domain (up to amino acid residue 1355) is involved in adhesion. The C-terminal portion of the β4 tail contains 5 tyrosine phosphorylation sites, including those needed for recruitment of Shc and PI-3K. Targeted deletion of the C-terminal portion of the β4 tail inhibited signaling through ERK and AKT, but not adhesion to laminin 5 and assembly of hemidesmosomes.
β4 integrin promotes endothelial cell migration and invasion, with the β4 substrate domain inducing the nuclear accumulation of ERK and NF-κB during endothelial cell migration (in vitro) and angiogenesis (in vivo). The β4 substrate domain has been identified as promoting tumor invasion and angiogenesis [Cancer Cell (2004) δ: 471-483].
Signaling by α6/β4 has been shown to promote bFGF and VEGF induced angiogenesis [Cancer Cell (2004) 6: 471-483]. Signaling by α6/β4 also promotes adhesion of keratinocytes through phosphorylation of PKB/Akt [J Invest Dermatol 123:444-451].
β4 integrin knockout mice exhibit a lack of hemidesmosomes and have severe junctional epidermolysis bullosa (epidermal blistering). β4 null mice were unable to survive more than a few hours after birth [J Cell Bio (1996) 134: 559-572]. In autosomal dominant polycystic kidney disease, kidney cysts demonstrate an overexpression of β4 integrin [Am J Pathol (2003) 163: 1791-1800].
By mediating tumor cell adhesion to endothelial CLCA2 (associated with colonization of the lung by breast cancer cells), β4 integrin is involved in the metastasis of breast cancer to the lung [J Biol Chem (2001) 276: 25438-35446]; [J Biol Chem (2003) 278: 49406-49416]. β4 integrin ligation to mCLCA1 (homolog to hCLCA2) activates focal adhesion kinase and mediates early metastatic growth of B16-F10 melanoma cells in the lung [J Biol Chem (2002) 277: 34391-34400]. β4 integrin also causes selective apoptosis in endothelial cells bound to tumor cells through activation of chloride channels. Endothelial cells incubated with β4 integrin undergo apoptosis [J Biol Chem (2001) 276: 25438-35446].
DPEP1
Dipeptidase 1 (DPEP1) (Swiss Prot Accession Number: P16444) is a GPI-anchored cell surface glycoprotein (homodimer) (J. Mol. Bio. (2002) 321: 177-184). DPEP1 has an extracellular domain that is typically about 369 amino acids in size.
DPEP1 is a zinc-containing enzyme that hyrdolyzes various dipeptides, antibiotics (b-lactams), and leukotrienes. DPEP1 is implicated in renal metabolism of glutathione and it conjugates. DPEP1 is expressed in the brush-border region of the proximal tubules of the renal cortex (Biochem. J. (1989) 257: 361-367). Cilastatin, an inhibitor of DPEP1, is commonly delivered with Imipenem, a b-lactam antibiotic, to inhibit breakdown in the kidney (J. Antimicrob. Chemother. (1983) 12: 1-35).
DPEP1 was determined to be >20-fold over-expressed in colon adenomas and carcinomas by SAGE analysis and localized to the epithelium of colorectal tumors by ISH (Cancer Research (2001) 61: 6996-7001). DPEP1 showed 2-fold or greater over-expression by relative RT-PCR in colon tumors compared to normal colon in 82% of patients tested, and over-expression observed in all stages of disease. DPEP1 was detected by RT-PCR in disseminated tumor cells purified from the blood and intra-operative lavage samples of colorectal cancer patients (Cancer Letters (2004) 209: 67-74).
Tissue Factor (TF)
Tissue factor (TF) is a cell surface glycoprotein with a large extracellular domain (typically greater than 200 amino acids in size). TF is the primary cellular initiator of blood coagulation where it serves as the cellular receptor for Factor VII. Signaling events linked to TF-Factor VIIa interaction can lead to tumor cell proliferation, transcriptional changes, altered cell-shape, and migration/adhesion.
TF is typically not expressed in cells that are in direct contact with the blood. TF is expressed in extravascular tissue, in fibroblasts and smooth muscle cells, where it serves as a haemostatic envelope outside the vasculature, poised to activate coagulation upon vascular injury. In vascular endothelial cells and monocytes, TF is typically absent, but TF is rapidly induced in response to inflammatory stimuli such as bacterial liposaccharide and inflammatory cytokines. Increased intravascular levels of TF have been reported in diverse pro-thrombotic syndromes such as myocardial infarction and sepsis.
Patients with malignant diseases are predisposed to hypercoagulation. Trousseau first reported the increased frequency of thrombosis in patients with gastrointestinal cancers in 1865, and subsequently this hypercoagulable state has been associated with TF. Correlation between elevated expression of TF and both advanced stages of malignancy and/or poorly differentiated tumors has been reported in several cancers including pancreatic, breast, colorectal, NSCLC, prostate, and glioma. Elevated expression of TF in tumors has also been correlated with other non-favorable prognostic indicators such as increased angiogenesis and multi-drug resistance. An alternatively spliced secreted form of TF has been detected in plasma that has elevated expression levels in normal samples (˜50 pg/mL) compared with tumors (50-350 pg/mL) in the plasma of breast cancer patients. For further information regarding TF, see Bogdanov et al., “Alternatively spliced human tissue factor: a circulating, soluble, thrombogenic protein”, Nat. Med. (2003) 9: 458-462.
Transfection of TF promoted metastasis in a melanoma mouse model, indicating a role for the cytoplasmic domain (Proc Natl Acad Sci USA (1995) 92:8205-9). Introduction of TF into a pancreatic adenocarcinoma cell line lead to both increased tumor cell invasion in vitro and primary tumor growth in vivo (Br J Surg. (1999) 86:890-4). TF knockdown by RNAi suppressed invasiveness of a pancreatic cell line (BxPC3) in vitro (Clin Cancer Res (2005)11:2531-2539). Humanized mAb (CNTO 859, 860) reduced metastasis (MDA-MB-231) to the lung from tail-injected 1000×, and also reduced tumor growth in a SubQ model (Centocor) (Journal of Immunotherapy. (2004) 27(6):S10). Anti-TF mAb (H36) abolished prostate (DU145) and reduced breast (MDA-MB-435) metastasis to the lung (Sunol/Dow) (Journal Thrombosis and Haemostasis (2003) 1 Supplement 1 July: #OC308).
NA/K ATPase Beta3
NA/K ATPase beta3 is a transporter involved in cellular metabolism and regulates a variety of transport functions in epithelial cells. NA/K ATPase beta3 has an extracellular region that is typically larger than 200 amino acids in size.
Blocking NA/K ATPase beta3 has been reported to sensitize tumor cells to pro-apoptotic stimuli.
Vasoactive Intestinal Polypeptide Receptor 1 (VIPR1)
Vasoactive intestinal polypeptide receptor 1 (VIPR1) belongs to the G-protein coupled receptor 2 family and has an extracellular domain that is typically greater than 100 amino acids in size. VIPR1 is involved in pulmonary and gastrointestinal vascular smooth-muscle relaxation, and VIPR1 ligand (VIP) analogs are in clinical development as bronchodilators for respiratory diseases such as COPD and asthma.
CD26
CD26 (dipeptidylpeptidase 4, DPP4, or adenosine deaminase complexing protein 2) is a type II cell surface serine exopeptidase that has an extracellular domain that is typically greater than 700 amino acids in size and which also exists in soluble form. CD26 is implicated in various biological processes including cell-matrix interactions, T-cell activation, inflammation, and regulating insulin secretion. Inhibitors of CD26 are in clinical development for type 2 diabetes.
CXADR
CXADR (coxsackie virus and adenovirus receptor; Swiss-Prot Accession Number: P78310) is a type I membrane receptor and a member of the immunoglobulin superfamily (Science (1997) 275; 1320-1323). CXADR has an extracellular domain that is typically larger than 200 amino acids in size. CXADR is a component of the epithelial apical junction complex that is essential for the tight junction integrity (J Biol Chem (1999) 274; 10219-10226). CXADR recruits intracellular PDZ domain-containing protein LNX (Ligand-of-Numb Protein-X) to intercellular contact sites (J Biological Sci (2003) 278; 7439-7444). CXADR may function as a homophilic cell adhesion molecule (Molecular Brain Research (2000) 77; 19-28). CXADR is involved in transepithelial migration of PMN through adhesive interactions with JAML located in the plasma membrane of PMN (Mol Biol Cell (2005) 16; 2694-703). CXADR functions as a receptor for group B coxsackieviruses and subgroup C of adenoviruses (AD2 and AD5); susceptibility to infection has been correlated with membrane expression level (Proc. Natl. Acad. Sci (1997) 94; 3352-56). CXADR knockout mice exhibited embryonic lethal phenotype associated with cardiac defects (Genesis (2005) 42; 77-85).
Over expression of CXADR has been observed in osteosarcomas and malignant thyroid tumors (Cancer Sci (2003) 94; 70-75; Thyroid (2005) 15; 977-87). CXADR is involved in mediating tumor formation in lung cancer cells; a CXADR antisense plasmid vector abrogated xenografts mediated by high expressing lung cancer cells and inhibited soft agar colony formation (Cancer Res (2004) 64; 6377-80). CXADR expression is enhanced after transition from preneoplastic precursor lesions to neoplastic mammary cancer outgrowth in a syngenic mouse tumor model (Clin Cancer Res (2005) 11; 4316-20). In a 3D tissue culture model of breast cancer cells, disruption of polarity and integrity, as in malignant transformation, can lead to up-regulation of CXADR (Proc. Natl. Acad. Sci (2003) 100, 1943-1948). CXADR overexpression in ovarian and cervical cancer cell lines enhanced cell survival by protecting against apoptosis (Clin Cancer Res (2005) 11; 4316-20). Expression of CXADR in gastrointestinal cancers correlated with tumor differentiation (Cancer Gene Ther (2006) Epub). Loss of CXADR expression associated with advanced bladder cancer (Urology (2005) 66; 441-6). Over-expression of CXADR in an ovarian cancer cell line inhibited cell migration (Exp Cell Res (2004) 298; 624-31). Expression of CXADR decreased in primary prostate cancer but is highly expressed upon metastasis (Cancer Res (2002) 62; 3812-8).
PTK7
Protein tyrosine kinase 7 (PTK7) is a transmembrane glycoprotein containing RTK consensus sequences that may function in kinase signaling, cell adhesion and signal transduction, and planar cell polarity (PCP) pathways. PTK7 has an extracelluar domain that is larger than 600 amino acids in size.
Macrophage-Stimulating Protein Receptor Precursor (MISTR)
Macrophage-stimulating protein receptor precursor (MISTR), also known as MST1R, MSP receptor, p185-Ron, CDW136, and CD136 antigen, is a receptor tyrosine kinase that has an extracellular domain that is typically larger than 800 amino acids in size.